Here’s Really Why You Get Butterflies in Your Stomach When You’re Nervous

This is what causes your tummy to fill with flutter.

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You’re about to go on that date you’ve been looking forward to all week, when all of a sudden your stomach flips and feels like it’s chock-full of a thousand frantic butterflies. Calm down in there, would ya?!

We all know that “butterflies in my stomach” feeling. It’s a common and totally normal feeling to have when you’re a little anxious. You may be able to recall a few instances when you’ve felt a tummy full of flutter, but do you know what’s actually causing it? (Hint: It’s not pretty winged bugs.)


The Gut-Brain Connection

To fully grasp the cause of that fluttery feeling, first, it’s important to understand the gut-brain axis. Hidden within your gut, you have what scientists call a “second brain,” or the enteric nervous system. The enteric nervous system that lives in your digestive system consists of two thin layers of more than 100 million neurons. These nerve cells line your entire gastrointestinal tract—from your esophagus to your rectum—and help regulate digestion. Even though this “second brain” doesn’t seem capable of forming thoughts (as we know them), it does communicate back and forth with the brain in your head.

And this gut-brain connection may explain why many people with digestive issues, like irritable bowel syndrome (IBS), are more likely to have depression and anxiety. This link also explains why when you’re stressed, anxious, or nervous, your digestive system bears the brunt too.


How Stress Affects the Digestive System

When your brain senses a threat or something unknown—whether it’s a big bear or a big presentation or even a big date—it triggers your sympathetic nervous system, which ignites your “fight or flight” stress response. This reaction sparks a cascade of physical changes to prepare your body to fight or flee. As part of the stress response, the sympathetic nervous system also starts up a conversation with the enteric nervous system in your gut. Here’s how it works:

When you’re stressed, three main glands gear up to cope with the situation. There are two glands in the brain, called the hypothalamus and pituitary glands, and a twin set that live atop your kidneys, called the adrenal glands. The brain glands tell your kidney glands to release the stress hormones epinephrine (also known as adrenaline), norepinephrine, and cortisol. These chemicals increase your heart rate and breathing, control your temperature, make you less sensitive to pain, and give you a burst of energy (which is very helpful for running away from said hypothetical bear).

To help give you the extra energy to conquer the perceived threat, your brain tells your gut to temporarily slow or even stop digestion. This pause in the digestive process may be why you forgot to eat before that big presentation, have “nervous poops,” or, you guessed it, feel those fluttering butterflies in your stomach.

While those butterflies in your belly may seem feel strange, they’re usually just a short-term reaction to stress. When the threat dissipates (like, after you crush that job interview), your body enters the calming “rest and digest” mode, which is triggered by the parasympathetic nervous system. This means your heart rate starts to slow, your digestive juices start to flow again, and the muscles in your gastrointestinal tract begin to relax. In layman's terms? Perceived threat and stomach butterflies have fluttered away. Phew.